Apparatus for the evaporation of materials in a vacuum



United States Patent Gottfried Geir Balzers, Liechtenstein 602,399

Dec. 16, 1966 Dec. 1, 1970 The Bendix Corporation Rochester, New York acorporation of Delaware Dec. 18, 1965 Switzerland Inventor Appl. No.Filed Patented Assignee Priority APPARATUS FOR THE EVAPORATION OFMATERIALS IN A VACUUM 2 Claims, 4 Drawing Figs.

U.S. Cl 219/271, 118/49, 219/121 Int. Cl F22b 1/28 Field 01' Search219/271- References Cited UNITED STATES PATENTS 9/1959 Lubszynski2,927,231 3/1960 Bucek 313/26 2,998,376 8/1961 Smith l18/49X 3,235,6472/1966 Hanks 13/31 3,277,865 10/1966 Smith 118/495 FORElGN PATENTS722,866 2/1955 Great Britain 118/49 1,010,456 11/1965 Great Britain118/495 OTHER REFERENCES Lentz, IBM Technical Disclosure Bulletin,Vacuum Evaporation Procedure", Vol.5 No. 1,.Iune 1962, p. 21.

Primary Examiner.loseph V. Truhe Assistant Examiner-C. L. AlbrittonAttorneys- Raymond J. Eifler and Plante, Arens, l-lartz, l-lix and SmithABSTRACT: The present invention consists of an electron beam apparatusfor melting and/0r evaporating metals in a vacuum such as in vaporcoating processes or the like. The improvement of this invention ischaracterized in that the support for the metal to be evaporated forms aseparation wall between an electron gun on one side and the material tobe melted on the other, thereby electrically and magnetically shieldingthe melt metal. The support is preferably of thin foil to suppress heatconduction losses which may also be reduced in thicker supportconstructions by spoked support design.

PATENTEDuan I976 3544763 SHEET 2 OF 2' INYENTOR. 116 .2 @5412, BY

APPARATUS FOR THE EVAPORATION OF MATERIALS IN A VACUUM Apparatus for theevaporation of materials is known in which a so-called electron gun isarranged in a vacuum chamber. The electron gun beam, by its action instriking the material to be evaporated, heats it and brings parts of itto evaporation. The vapors so produced can be condensed to coatsubstrates arranged in the neighborhood with the mentioned materials,for example, glass plates, optical lenses and electron microscopespecimens. A great advantage of the electron beam evaporation lies inthe fact that an electron beam can be concentrated so that with suffcient focussing on a very small surface, a high energy density can beattained with a reasonable output and, thereby, a high temperature.Further, an electron beam can be easily deflected by electric ormagnetic fields and, for example, can be directed alternately ontodifferent materials which has significance for the production of mixedcoatings. The energy carried over to the evaporation material isconveniently and accurately controllable with electron beam heating,which is important for the automation of evaporation equipment.Surprisingly, it has been shown that it is also possible to evaporatenonmetals with the electron beam, for example, quartz. The electron beamwould represent the ideal means for the vacuum evaporation of materialof this kind were it not also associated with some seriousdisadvantages.

One disadvantage arises from the unavoidable ionization of vapors by thebeam. This can have, as a consequence, an asymmetric charging of thesubstrate, which often leads to condensation with undesirabledistribution or structure. In order to overcome this disadvantage, ashas already been proposed, a metallic gauze or grid is arranged as ascreening electrode between the vapor source and the surface to beevaporated on for the purpose of intercepting the annoying chargecarriers, electrons or ions. Unfortunately, it becomes evident that adevice of this kind, placed in the path of the vapor, brings with it asa disadvantage the danger of shadowing parts of the condensationsurface. Also, if the mesh of the gauze or the spaces between the wiresof the grid are too large, it becomes too inefficient. On the otherhand, if the spaces between the gauze or grid are too small, they cangrow together as the result of condensation.

Another disadvantage of the electron beam arises from the fact that itis unavoidably associated with electric and magnetic fields. First ofall, these fields can quite generally impair any electrical measurementsin the evaporation equipment. They are especially disturbing if onewishes to undertake condensation on the substrate in quite definitelyoriented electric or magnetic fields, as for example, in the productionof magnetic thin films with prescribed preferential direction ofmagnetization (for storage elements of computers) or in the productionof optically polarized layers by the evaporation of dielectrics indirected electric fields. The mentioned fields are also disturbing whenelectron-optical experiments should be carried out on an evaporatedlayer in the formative state.

The present invention has set as its object an apparatus with thepractical advantages of electron beam evaporation without limiting itsutilization by the aforementioned disturbing disadvantages. Theapparatus according to the invention relates to the evaporation ofmaterials in a vacuum through electron bombardment and is characterizedin that the support serving for the evaporation carrying the evaporationmaterial is formed as a part of the separating wall electricallyshielding two regions of space from one another. The apparatus forheating the separation wall by electron bombardment is provided in theone region of space, while the side turned away from this apparatus isformed for the reception of the material to be evaporated.

The use of the invention has the advantage as compared with the directbombardment of the evaporating surface of the material that essentiallythe heat transfer must only be effective on the material to beevaporated and the heat leakage through the support can be kept verysmall in contrast to all other known heating processes. In the knownmethod of resistance heating, for example, with a tungsten strip servingas a material support, the heat produced by the current flowing throughit is uniformily distributed over the whole surface of the heatingribbon. Only a small part of this surface, which stands in directcontact with the material to be evaporated, is useable as a true supportfor the transfer of heat. At least percent of the heat energy producedgoes off by free radiation and is lost by the conduction of heat to thetwo connecting electrodes. In contrast, with electron beam heating, onemay limit the production of heat to that place on the support where itis immediately transferred to the material to be evaporated. Since thepart of the support not covered need not be subjected to the electronbombardment, the radiation loss can be held substantially smaller.

BRIEF DESCRIPTION OF THE DRAWING FIG. I shows an embodiment of myinvention wherein the evaporation support may be formed of an electricalconductor such as metal, carbon, graphite, or the like.

FIG. 2 shows an embodiment of my invention utilizing a cooled,double-walled return-current shell in which the evaporation support maybe a nonconductor of electricity.

FIG. 3. shows an evaporation shield for use with my invention.

FIG. 4 shows the embodiment of FIG. I to which has been added means forproviding change of the evaporation shield and material.

A first example of the application of the invention is illustrated inthe accompanying FIG. I. The apparatus is built up on the flange 1 whichcan be secured in an opening in the baseplate ofa vacuum evaporationequipment. The numeral 2 designates an annular-shaped sealing groovewith an elastic sealing ring (O-ring gasket) 3, 4, a cylindrical,electrically-insulating part, for example, of porcelain, 5 a cylindricalmetal shell surrounding the part 4, and 6 a hot cathode which issupplied with heating current through the vacuum tight,electrically-insulated feedthroughs 7 and 8 from the source 9 and with anegative accelerating potential for the electrons of a few one hundredto a few one thousand volts. On the metal shell 5, which stands inelectrically-conducting connection with the flange 1, there lies a thinmetal disk 10 of a refractory material (metal) which serves as anevaporation support for the material to be evaporated and is provided inan advantageous way with a depression II for the receipt of the same.

In operation, the electrons emitted from the cathode 6 are acceleratedonto the evaporation support 10 and heat it according to the energytransferred. The inner wall of the electrically-insulating part 4receives a negative surface charge through scattered electrons, whichconcentrates the beam current to the extent that it only strikes thepart of the thin sheet 10 which serves for the evaporation. Obviously,more complicated known electron optical electrode arrangements can alsobe used in order to produce a sharply-focussed electron beam on theplace of evaporation.

The thinner the thin plate 10 is chosen, which serves as the evaporationsupport, thebetter one can preserve the known advantages of theconventional kind of electron beam heating without having to count thecost of its disadvantages.

Any known electrically-conducting refractory material can be used as thehigh temperature stable material for the part of theelectrically-shielding separation wall serving for the evaporation whichexhibits a sufficient mechanical strength. Those known materials to beconsidered first are those usually used for evaporation with resistanceheating, such as tungsten or molybdenum sheet or else foils. Also,nonmetals, for example, plates of carbon, graphite and carbides etc. maybe used. Nonconductors of electricity can also be used, for example,plates of oxides if an electron gun with a focussed beam is used for theelectron bombardment, such as, for example, provided in the arrangementshown in FIG. 2 as will be later described. The auxiliary electrode 26can be eliminated and the return current flow from the point ofbombardment by the electrons on the insulating support 25 results fromthe scattering or thermal emission of electrons which are collected bythe neighboring parts of the inner walls of the shielding 20.

The metal shell 5, together with the thin sheet form anelectrically-shielding separation wall between a region of space A,containing the cathode 6 and the space region B in which the evaporationtakes place.

The regions of space A" and B are not only electrically shielded onefrom the other, but also largely magnetically shielded. The return flowof the electron beam current going out of the cathode 6 is uniformlydistributed radially over the disc 10 and along the shell 5. Themagnetic effect of the electron current and the return current largelycancel each other in this way. In order to eliminate the magnetic effectof the cathode coil 6, it must be built free of induction, for example,it is built up as a double winding as is well known.

In order to almost completely eliminate the magnetic effect of the beamcurrent and the cathode heating current, one can, within the scope ofthe invention, also make use of the known magnetic shielding materials.An additional shield of such material may be provided that substantiallysurrounds the space A" where only an opening for the exit of the vaporstream produced must be left free. One can also manufacture the flange land the shell 4 of FIG. 1 themselves out of magnetically shieldingmaterials so long as the return current is not too great, consideringthe poorer electrical conductivity of these materials.

Another form of application of the invention is shown in FIG. 2. It isdifferentiated from FIG. 1 by a differently-formed double-walled returncurrent shield 20 into whose annular hollow space a cooling medium isled, through the conduit 22 and out again through another conduit 23.The electrode 26, held at the same or higher negative potential than theelectron emitting hot cathode, is provided in order to concentrate theelectrons escaping from the cathode 24 onto the evaporation support 25.The gap between the electrode 26 and the neighboring wall of the returncurrent shell 20 is made so small that no electrical gas discharge canappear. It is well known that this will be the result if the theoreticalmean free path length of the electrons in the gas situated in the gap issubstantially greater than the gap width (gap widths of 1 mm. aresuitable in most cases). The electrode 26, for example, of copper, canbe so formed that it acts as a concave mirror for the heat radiationemitted from the cathode. Thus, heat is focussed back onto the cathodewhich produces a better utilization of the energy.

The two previously-described examples have the advantage that thoseparts of the separation wall serving for the electrical shielding andwhich serve for the evaporation are very easily replaced and withoutgreat expense. Since the sheet serving as the evaporation support isthin and its forming cost is low, in

contrast to the production of boats for evaporation, which must be madeof the same refractory metals, such as tungsten or molybdenum, one worksvery economically according to the invention on these grounds.

The evaporation support itself can exhibit different forms, for example,for the purpose of the least possible heat conduction, it can be formedof tightly woven wire mesh where the melt of the material to beevaporated is held together by its surface tension.

FIG. 3 shows, in an enlarged sketch, a form of the application in whichonly the central part 31, carried by the narrow spokes 30 serves as theevaporation surface and it likewise has the advantage that theconduction of heat from the evaporation surface is solely through thespokes and is very small, particularly since the return current flowsthrough them and thereby warms them. For that reason, one may also use athicker sheet which results in a longer useful life. It is evident thatthe small cutout portions 32 will markedly influence the electricalshielding of the separation wall.

In many applications, the longest possible useful life of theevaporation support plays a decisive role (although they are cheap andeasy to replace) namely when a greater amount of material should beevaporated without the necessity of breaking the vacuum. In these cases,one can use an arrangement as is shown in FIG. 4. This example shows arelatively similar construction of the electron beam producing apparatusas that in H0. 1; however, the evaporation support is formed as anannular channel 40 in a rotating disc 41. Through this, one gains notonly a greater heating surface which can receive more evaporationmaterial 42 at one time, but one can, for example, provide an additionmechanism 44 to the annular channel which is indicated as a funnel inFIG. 4.

lt should be mentioned further that the invention is especially suitablefor the recently used multiple flash evaporation technique for theevaporation of mixtures in which the intermittent use of very highelectron beam currents is necessary. The electric and magnetic fieldsoccuring in this case disturb not only on account of their absolutemagnitude, but also because of their time variation through whichundesired changing potentials are produced in electrical conductorswhich can be very disturbing to measurements.

lclaim:

l. An apparatus for evaporating in a vacuum a material disposed upon asupport, comprising:

means for generating an electron beam; and

an electrically conducting housing having integral outer and innerwalls, said inner wall spaced from and surrounding said electron beamgenerating means so that no electrical gas discharge can appeartherebetween, said inner wall is further formed to position saidmaterial support so that the material located therein may be vaporized.

2 An apparatus as recited in claim 1 wherein said inner and outer wallsform a chamber having means for receiving and discharging a coolant sothat when said material is vaporized by said electron beam generatingmeans said housing may be cooled.

